1. Field of the Invention
This invention relates to an optical disk recording and reproducing device adopting an interleave processing executed on digital signals for error correction and, more particularly, to a recording and reproducing device for musical information that is digital and uses an optical disk as a record medium.
2. Description of the Prior Art
Compact Disc or CD techniques wherein musical information is converted into digital signals to be recorded thereon has been utilized as a music source with high quality, and recording/reproducing devices for the CD techniques have also been evolved for practical use.
Meanwhile, an optical disk recording/reproducing device, that differs from the CD, wherein a recording format with compatibility is adopted and digital audio data are recorded and reproduced using a recordable type optical disk as a record medium is disclosed for example in our preceding PCT application (Appln. No. PCT/JP87/00764).
In the optical disk recording/reproducing device, as shown in FIG. 1, an opto-magnetic disk 1 wherein a vertical magnetizing membrance with a magneto-optical effect is provided on a disk recording surface that is 12 cm in diameter is used as a record medium. There are tracks in the opto-magnetic disk 1 spirally formed by the respective pre-groups 2 each one of which is .lambda./8 in depth (in which .lambda. indicates a wavelength of a laser beam). In each land section placed between the pre-groups 2, a pre-recorded area 4 on which pits 3 or frame signals are recorded in the circumferential direction presenting uneven shapes at regular intervals. In the center part of the pre-recorded area 4 there is a data record area 5 where the opto-magnetic recording is performed.
Also, in a lead-in section of the inside circumference of the opto-magnetic disk 1, there is provided an area called TOC (table of contents) section 6 on which various data indicating the recorded information of the disk, for example, numbers of musical pieces, starting and ending times, can be recorded.
The distance from the pit 3 provided in the pre-recorded area 4 to the pit 3 provided in the next pre-recorded area 4 corresponds to one frame, wherein 588-channel-bit data, being in conformity with a CD standard, can be accommodated.
In the CD standard, EFM modulation (Eight to Fourteen Modulation) is adopted. That is, one frame consists of 588 channel bits, with the first 24 bits being allotted to frame synchronous signals, while the remaining 14.times.32 bits (32 symbols) are allotted to the musical information data and parity bits. Thus an error correction code called CIRC (Cross Interleave Reed-Solomon Code) supplying the interleave delay which corresponds to maximum 108 frames is performed.
The CIRC error correction is executed, in addition to adopting EFM modulation, in such type of optical disk recording/reproducing device using the recordable optomagnetic disk 1, in order to enable reproduction of a usual CD and to attain upper compatitility.
Though the detailed explanation is abridged, the conventional CIRC error correction adopted for CD is executed by two-series Reed-Solomon Code that includes C.sub.1 error correction, for correcting a one word symbol code, and C.sub.2 error correction, capable of correcting data scattered within the plural frames, due to interleaving. By this code, in case erroneous data is found in the recorded data of an optical disk upon reading, the error can be corrected by referring to the data placed in 108 frames before and behind the erroneous data.
With reference to FIG. 2(a), illustrating an analog waveform of the recorded musical information, new musical information B is written from the time t.sub.0 into the prerecorded musical information part A for example. When these recorded information are reproduced, as seen from FIG. 2(b) illustrating an analog waveform of the reproduced musical information, an abnormal sound (consisting of noise and sometimes referred to as buchi-buchi sound) originates during the period .DELTA.T that includes several frames before and after the time to.
This abnormal sound is caused by the above-mentioned C.sub.2 error correction. That is, since the interleave relevancy is lost in said period .DELTA.T, the wrong correcting procedure is performed to cause the abnormal sounds as though the musical information A and B are alternately outputted per one sample.